This invention relates to a multi-layered drainage sieve or fabric formed by splicing the ends together with a binder warp, and to a method of so splicing the ends.
German (OS) No. 2,455,184 discloses endless woven multi-layered drainage forming sieves for use in paper manufacturing. This German application also teaches that such drainage sieves may be woven in flat form and then joined end-to-end, but it does not disclose the method by which the ends of flat, multi-layered drainage sieves can be spliced together.
The problem of end-to-end connection does not arise with drainage sieves that have been woven endless to begin with. However, endless woven sieves have the disadvantage that the sieve length is predetermined and there are generally fewer possibilities for variation of the fabric count and the number of filling threads, so that the drainage capacity is only adjustable to a limited extent. Therefore, endless weaving requires considerable machinery to meet customers specifications. On the other hand, flat woven papermaking sieves can be produced on a single loom in any desired length. By varying the number of filling threads and thread diameters the customers specifications can be met more adequately. In general, these advantages of flat weaving outweigh the disadvantages inherent in connecting the ends of the sieve. There is thus a need for multi-layered, spliced drainage sieves and for a method of joining the ends thereof.
In principle, the ends of a multi-layered drainage sieve can be joined in the same manner as a single-layer drainage sieve, e.g. by simply machine sewing the ends together, either with a fabric connecting seam (German OS No. 2,700,390) or by a pin seam. In principle, it is possible to join the ends of a multi-layered drainage sieve with a woven seam as is commonly known for single-layer drainage sieves. A device for joining the ends of a single-layer drainage sieve is described in German AS No. 1,710,205. In joining the ends of a multi-layered sieve with a woven seam, the binder warp may even be inter-woven in the region of the seam. However, practice has proved that such a multi-layered woven seam is difficult to produce without any defects.
German OS No. 2,429,162 discloses a method for joining the ends of multi-layered sieves in which a plurality of zones are provided where the warp threads are freed from at least one weft layer to increase the flexibility of the seam which, in principle, is a pin seam. Multi-layered sieves which have been joined in this manner have the disadvantage that the drainage capacity in the seam region is substantially less than in the remaining sieve area.
German OS No. 2,707,705 describes a method for joining the ends of a multi-layered sieve in which free fabric ends of different layers are overlapped and joined by sewing, stapling, gluing or interlocking with a (Velcro) tape fastener. However, these modes of connection do not sufficiently ensure the absence of marks on the paper.